Method of fabricating seamless steel pipes

ABSTRACT

A process for the manufacture of seamless steel tubing comprising continuous casting rectangular cross-section bars, cutting the bars into billets, heating the billets, upsetting and piercing the billets into hollow circular cross-sectioned blanks, hot extruding the blanks into seamless tubes and stretch reducing the seamless tubes where necessary.

United States Patent Sejournet et a]. 51 Oct. 17, 1972 METHOD OF FABRICATING 2,083,466 6/1937 McLay ..29/527.6

SEAMLESS STEEL PIPES 3,365,791 1/1968 Olsson ..29/527.6 1 2,107,510 2/1938 Skinner et al ..29/527.5 [72] 93R?" 3: 313 2,218,458 10/1940 Wright ..29/527.7 S g 3,581,384 6/1971 Petersen et a1. ..29/527.7 3,038,250 6/1962 Porterfield ..164/76 x [73] Assignee: Cefilac, Paris, France Primary Examiner-John F. Campbell [22] Sept 1970 Assistant Examiner-Donald C. Reiley, Ill [2]] Appl. No.: 75,273 Attorney-Webb, Burden, Robinson & Webb [57] ABSTRACT [30] Foreign Application Priority Data A process for the manufacture of seamless steel tub1ng Sept. 25, France comprising continuous casting rectangular cross-section bars, cutting the bars into billets, heating the bil- Cl I 47, 164/76, lets, upsetting and piercing the billets into hollow cir- 164/82 I cular crosssectioned blanks hot extrudingthe blanks [51] Int. Cl. ..B23k 19/00 into seamless tubes and stretch reducing the seamless [5 8] Field of Search ..29/527.5, 527.6, tubes where necessary. DIG.47; 164/7 6,82,270 [56] References Cited 7 Claims, No Drawings UNITED STATES PATENTS I V 3,636,605 l/l972 Vitcha et a1. 29/5275 METHOD OF FABRICATING SEAMLESS STEEL PIPES BACKGROUND OF THE INVENTION Our invention is directed to an improved process for obtaining seamless steel tubing and, more particularly, a process for converting continuous cast bars into seamless steel tubing of substantial length and with a minimum number of processing steps.

Prior to the substantial developments in continuous casting, seamless steel tubing was generally produced by breaking down an ingot through hot working into a bloom and then in subsequent operations reducing the bloom ultimately into a round billet which was then directed through various piercing mills, plug rolling mills, reeling machines and sizing machines. Depending on the size of the end product some operations were repeated, e.g., two piercing mills, and there were many intermediate heating operations as well as other operations such as rotary. rolling mills which were employed.

With the advent of continuous casting, a rectangular cast bar of generally 4 to 12 inches in cross-section is produced. Because of the cast structure and rectangular cross-section and the previously known operations which employed a wrought structure and a rounded cross-section, it was reasonable to produce seamless tubing by breaking down the cast bar into a round bar of wrought structure through rolling operations and proceed with the operations employed prior to continuous casting.

Attempts have been made to employ the cast bar as a starting material and eliminate some of the conventional processing steps. One solution included cutting the cast bar into billets, heating the billets and then forming round blanks which are made hollow by hot piercing, elongating the blanks on known equipment to reduce mainly the outside diameter and to a lesser extent the wall thickness, cutting the hollow product in several parts which are rolled on mandrel mills to reduce mainly wall thickness and to a lesser extent the outside diameter, and then sizing the outside diameter on a stretch reducing mill. Various push benches, rolling mills and extrusion presses were employed to obtain the product for the mandrel mills.v

Such a solution with its many operational steps results in cummulative problems. Tool wear occurs in each operation and since the requisite intermediate beatings and descalings increase as the number of mechanical processing steps increase, the metal yield is very low. These cummulative problems raise the cost of manufacture to the point that any gain obtained by the continuous casting is lost in the modified processing. Of equal importance is that the quality of the products suffers since the more operational steps, the more chance for internal and external damage to the product.

Our invention avoids all the drawbacks of the previously tried processes for producing seamless tubing and results in a high quality product manufactured with a minimum of processing steps and with a maximum yield of metal from the cast bar to the finish product. Therefore, not only is a cost savings realized by the use of the continuous cast bar, but the cost savings is substantially increased by the high metal yield, good quality product and the elimination of the many processing steps employed heretofore.

Briefly stated, our process includes continuous casting a bar, cutting the bar into billets, heating the billets, upsetting and piercing the billets into hollow circular blanks, hot extruding the blanks into tubes and reducing the diameter of the tubes on a stretch reducing mill where necessary.

Our invention permits the utilization of all steels which can be continuously cast for manufacture into seamless steel tubes having diameters greater than .8 inches and wall thicknesses above .120 inches. It is understood' that continuous casting produces bars of square or rectangular cross-section and as used herein, rectangular cross-section is employed to cover both cross-sections.

Initially the steel is continuous cast into rectangular bars which are cut into billets. This cutting can be done by flame cutting on the casting machine with the length corresponding to the weight to be extruded. i

The billets are then heated to a temperature of about l830 to 2280 F as is appropriate for the particular steel type and then descaled. The billets can be immediately reheated from the casting step, thereby retaining the casting heat and minimizing the amount of additional heat input from the reheating operation.

The reheated billets are then inserted into a round container of a piercing press where they are first upset and then pierced and severed from the piercing discard. The upsetting-piercing operations are advantageously carried out with the aid of a glass-like lubricant. The resultant blank is cylindrical, thatis, circular in cross-section and hollow.

The blanks can then be sent to the extrusion press without intermediate heating, provided the extrusion press is of sufficient power to handle them. Of course, the larger the blanks, the slower the cooling rate, and this, along with efficient handling techniques and proper positioning of equipment, further aids in eliminating any intermediate heating. The blanks are hot extruded into seamless tubes of relatively large diameter.

Where the desired diameter of the product is small, the product from the extrusion press is sent into a stretch reducing mill to reduce the diameter and adjust the wall thickness to the precise desired size. The temperature of the tube running into the stretch reducing mill may be maintained and kept as a constant value by employing an in line furnace at the exit end of the extrusion press. I

Where the long tube exiting the extrusion press has the desired diameter for the final product the stretch reducing mill is not needed.

Our process, therefore, takes advantage of the upsetting, piercing and extrusion operation to admit as starting material a rectangular billet with an internal cast structure. It can be seen this process is conducted with a single reheat step and since there is a minim um of processing steps, the cast bar to seamless tube metal yield is high. In addition, the metallurgical properties are excellent and the surface condition is improved because of the elimination of handling and various mechanical processing steps. The modern industrial extrusion press is capable of handling heavy blanks and the hourly output compares advantageously with the various large tubing mills, as well as welded tubing in stallations.

In fact, the hourly output from the upsetting piercing press and the extrusion press may be high enough and tube sizing critical enough that it may be advisable to operate two stretch reducing mills in parallel downstream of the extrusion press.

Our process can be applied to all the various steels produced by continuous casting and for this reason and all the reasons set forth heretofore, it will be recognized that an improved seamless tube can be manufactured at a cost rate below that achieved heretofore.

We claim:

1. A process for manufacturing seamless tubes in all grades of steel from cross-sectionally rectangular bars I having a cast structure and not a wrought structure,

2. The process of claim 1 wherein the transforming of the billet into the circular cross-sectioned and hollow blanks includes initially upsetting and then piercmg.

3. The process of claim 1 including after hot extruding the steps of stretch reducing the seamless tubes on a stretch reducing mill to reduce the diameter of the tubes and adjust the wall thickness to obtain precision tolerances of the tubes.

4. The process of claim 1 wherein the cutting step A and the heating step B taken place immediately after the continuous casting operation, so that the majority of the casting heat is retained and the heating step B is minimized.

5. The process of claim 1 wherein a glass lubricant is employed in at least one of the transforming step C and the hot extruding step D.

6. The process of claim 1 including the step of heating the hollow blanks before hot extruding.

7. The process of claim 3 including the step of passing the seamless tube through a heating furnace before stretch reducing.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. g bog 7a Dated October 17,1972

Inventor(s) Jacques Sejournet et a1.

It is eertified that error appears in the above-identified patent and that said Letters Patent are hereby corrected asshown below:

Under item 30 the priority date should read --Sept. 25, l969--. Y v v Signed and sealed this 1st day of May 1973.

(SEAL) Attest:

EDi-JARD M. FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC 60376-P69 v Q IJ.S. GOVERNMENT PRINTING OFFjCE: [969 0-356-334 

1. A process for manufacturing seamless tubes in all grades of steel from cross-sectionally rectangular bars having a cast structure and not a wrought structure, which bars issue from a continuous casting installation and have not been subjected to any intermediate metalworking steps, said process comprising in sequence: A. cutting the bars into billets of a desired weight; B. heating the billets to deformation temperature; C. transforming the billets into circular cross-sectioned and clear through hollow blanks in an upsetting-piercing press; and D. hot extruding the blanks into seamless tubes of desired dimension.
 2. The process of claim 1 wherein the transforming of the billet into the circular cross-sectioned and hollow blanks includes initially upsetting and then piercing.
 3. The process of claim 1 including after hot extruding the steps of stretch reducing the seamless tubes on a stretch reducing mill to reduce the diameter of the tubes and adjust the wall thickness to obtain precision tolerances of the tubes.
 4. The process of claim 1 wherein the cutting step A and the heating step B taken place immediately after the continuous casting operation, so that the majority of the casting heat is retained and the heating step B is minimized.
 5. The process of claim 1 wherein a glass lubricant is employed in at least one of the transforming step C and the hot extruding step D.
 6. The process of claim 1 including the step of heating the hollow blanks before hot extruding.
 7. The process of claim 3 including the step of passing the seamless tube through a heating furnace before stretch reducing. 